Cholesteric Unwinding at the Phase Transition

The cholesteric mesophase begins to unwind prior to the phase transition from this phase to a higher density hexatic phase. The unstructured birefringent cholesteric areas in the photomicrograph above are represented by several shades of blue color. As the mesophase completes its unwinding, birefringence acquires higher order colors as seen in the purple area adjacent to the hexatic region. The DNA concentration for this specimen was initially 100 milligrams per millimeter, but this changes as the solvent evaporates. The magnification is approximately 400x. Originally recorded on Fujichrome 64T transparency film using a Nikon Optiphot-Pol microscope with crossed polarized illumination, the image above was digitized using a Nikon CoolScan transparency film scanner. Exposures were recorded about 3 f-steps under the recommended value given by an in-camera photomultiplier and were push-processed approximately 1.75 f-steps in the first E-6 developer.